A US Air Force MQ-9 Reaper drone sits in a hanger at the Amari Air Base in Estonia on July 1. SeaGuardian drones, which are also manufactured by General Atomics Aeronautical Systems, are similar to Reaper drones.
Photo: Reuters

The US is negotiating the sale of at least four sophisticated aerial drones to Taiwan for the first time, aircraft that can keep watch over huge swathes of sea and land, six US sources familiar with the negotiations said.